GEOLOGIC INVESTIGATION SERIES I–2650 U.S. DEPARTMENT OF THE INTERIOR Prepared for the ATLAS OF : THAUMASIA REGION U.S. GEOLOGICAL SURVEY NATIONAL AERONAUTICS AND SPACE ADMINISTRATION SHEET 1 OF 3 85° 90° 80°

95° 75° VALLES NO. CRATERS LARGER CHANNEL-SYSTEM MARINERIS WESTERN VOLCANIC CIRCUM-ARGYRE CRATER THAN 2, 5, AND 16 KM Hr HNf AND PLATEAU AND HIGH-PLAINS ASSEMBLAGE SYSTEM INTEROR ASSEMBLAGE MATERIALS MATERIALS DIAMETER ° HNf 70 EOLIAN MATERIALS 100 ° DEPOSITS PER 1,000,000 KM2

THARSIS 2516 MONTES Hsu Hsl2 HNf FORMATION ° 65 Al 105 ° 40 or less HNf HNu Hsu HNr Avfs 50 c1 Avfs ° THAUMASIA 60 110 SINAI PLANUM Hr ° 60 Hsl1 cs 70 PLANUM HNr At5 Avfs HNf 80 c2 HNu 90 ° 55 115 cs Avfs ° Hsu 13 Avfr 100 ° –15 –15 ° Nf Avfs Nb Nf HNr Npl Hf 2 cs Nplh At5 Hr Nfc Avfr 150 Hr c Hf 2

Npld 200 2 Hsl2 cs Hr

Hf c d 1 Npld Nfd Hsl1 Npl Nfc Hsl2 2 HNr Nfc AHt3 Solis 300 50 Nb Nf Hsl AHt Nb 1 3 SYRIA Hsl1 Planum PLANUM ° d d –20 FORMATION –20 HNr ° 400 Daedalia Npl Nf 2 Hsu Nb 75 Hsl2 FRACTURED Hf 500 Nfd MATERIALS Hsl1 DISSECTED Hf AND ETCHED Hr c1 Nf Ht PLATEAU MATERIALS HIGH-PLAINS 600 100 Hsl2 HNt 2 Hf HNr Npl Ht1 SEQUENCE MATERIALS Planum Hpl3 2 Nf Hsl1 HNt 700 Nplh d Nf FLOW Hpld AND Hr 800 Nfc Nf Hch CONSTRUCT c2 Nb Nf c Nfc 1 MATERIALS Hpl3 HNplt 900 150 d Npld Nf Hr Hpl3 cs Hsl1 HNt 1000 Hf HNt HNr HNcht Hsl1 d Nb c Ht2 Nb 1 HNpld HNr HNafs 1200 200 25 d Hr HNt Hpl HNf HNf HNt 3 Nb Npld –25 HNfc HNu ° Nf –25 HNt ° Nf c HNt Npld Hsl1 1 17A HNade HNf HNplt Npl2 Hf Nb Nb d HNf HNt 9A 300 75 Nfc Nf c Nfd Nplh c 1 3 Npl2 Nfd 1 Nplh AHt Nf HNf c 1 Hpl3 Nf Nfd Npld Nple 14 Nfd 10 Nb Nf Nb HNf c HNpld HNplt Nf 400 100 Nf 1 Hpl c1 cs 3 HNf c HNf 1 Npld HNpld Nfc c1 Nb HNf c 2 c Npl1 Nplh Hpl3 Nple Hpl 1 500 Ht2 c1 3 Nf d Hr Npl2 Nfd Nf Hpl Nfd 3 600 150 Npl2 HNf Npld n c1 Nplh Nfc Nfd HNf Nplh HNf c a Nplh 2 Nfd Nfd Nak c2 l ° –30 –30 Npl ° 200 T 2 c1 cs HNcht h Hpld Nplh Hpl3 HNf Nf Nplh Nplh Hpl3 h cs Hpld Nah 3 c1 g Nplh 2 Hpl Nb Hpl3 Nb 2 Npl 250 Npl a HNf HNf Nb i Hpl3 Npld Nb Hpl Npl cs HNcht c 3 c u 1 Nfd 2 1 Nfd H HNf c Nfc m Nfd c 1 Hpl3 2 cs Nplh c1 Hpl c Nf 3 2 a Nb Nplh Hr HNf Nf Nf a s 19 Hpl 3 Hpl3 Npld Nb i c1 i c Nf HNfc Hpl 2 1 HNt Npld 3 Nah Npl HNf a Nf Npl more highly modified by fluvial and sapping processes and sediment deposition. Cuestas and Basin-rim unit—Material of Argyre basin rim. Rugged, hilly material that in part resembles hilly c1 c1 s Nb Hpl3 2 hog backs formed by differential erosion of tilted beds of warped and extended crust unit (unit Nplh) and basement complex (unit Nb). Unit not recognized by Scott and Tanaka c1 H Nfd a Npld Nf Npl1 Older fractured material—Similar to intermediate-age fractured material but more rugged, (1986). Interpretation: Materials uplifted by the Argyre impact event Nb 4 Hpld Npl2 i m faulted, and cratered; deformation has destroyed primary morphologic characteristics 2 Nfd g c CRATER MATERIALS Ht c Hpl 1 Npl Nb h Nf 1 3 u 1 Basement complex—Forms knobs, mesas, and broad areas of prominent relief similar to hilly ° –35 unit but characterized by highly complicated structure of undifferentiated material; dissected in [Impact craters are assigned relative ages on basis of morphologic appearance and superposition relations. With increasing –35 l ° a HNf a HNf Npl age, craters become progressively more degraded and subdued in appearance, and their ejecta deposits are discernible only c1 Nplh places; embayed and (or) partly buried by materials of several younger units of the plateau and c1 n Nplh 2 HNfc h Npld HNade high-plains assemblage and Syria Planum and Montes Formations. Interpretation: near rim crest. On correlation of map units, overlaps are indicated between crater-age classes and time-stratigraphic bounda- Hpl3 Hpl3 d Nf HNf c 1 ries. Craters with rim crests mostly >50 km in diameter are mapped. Scott and Tanaka (1986) did not separate 7 Nb T Assemblage of undifferentiated rocks of many origins, which may include igneous and meta- 1 Hch Hpl3 materials into three separate units] Npl Nfd c1 cs morphic rock outcrops and impact breccia, comprising complicated tectonic structure Nfc Nb HNade c c1 HNr c Nplh 1 cs Smooth crater floor material—Forms smooth to moderately rough floors of most impact craters HNf 1 Dissected and etched materials—Dissected and etched materials include the eroded rock and Nb Nfd Nplh c1 Hpl that have continuous rims. Interpretation: Mainly eolian, mass-wasting, or fluvial deposits Nfc 3 superposed sediment deposited by the resurfacing agent because they generally cannot be map- Hpld cs Hpl HNfc 11 HNf c1 3 ped separately; their relative-age ranges reflect both materials. The origin and rock type of the largely of Amazonian age Nfd HNcht Hpl HNpld 3 eroded rock are only inferred in most instances because channels and furrows have modified c2 Material of fresh to subdued craters—Slightly to moderately eroded craters having continuous Nf Nf Nak HNf Hpl Npl Npld original surface characteristics rims and ejecta blankets that extend at least one crater diameter beyond rim crest; central peaks 3 1 cs Nb Hpld 12 c1 8A HNr Younger dissected material—Areas of relatively young smooth materials along parts of the or central pits in places. Superposed on member 1 of the Tharsis Montes Formation and smooth c1 HNf c1 southern margin of the Thaumasia plateau; dissected by small, sinuous valleys and valley net- unit, intermediate and older fractured materials, fractured and dissected material, older ridged Nfd Hpl c Ht1 3 2 works that trend downslope from the Thaumasia highlands and southern part of the Coprates plains material, and subdued cratered and cratered materials of the plateau and high-plains HNpld cs c Npl1 Nb 1 cs HNade rise toward low-lying regions. Type area: lat 34.5° S., long 71°. Unit not recognized by Scott assemblage c1 Npl Nak 1 ° –40 and Tanaka (1986). Interpretation: Relatively young, alluvial and colluvial deposits, which may c1 Material of degraded craters—Deeply eroded craters; rims commonly incomplete; central peaks –40 ° Ht1 c include older rock surfaces, modified by fluvial and sapping processes scarce. Often embayed by Upper Noachian and younger materials 2 Hpl cs cs Hpl3 Nfc cs 3 HNplt Troughed material—Moderately cratered, uneven surface dissected by numerous large troughs cs HNf HNf c1 HNf HNf Hpl3 Hpl along the southeastern margin of the Thaumasia plateau centered at lat 29.5° S., long 61.0°; Contact—Dashed where approximately located or gradational c 3 1 Hpl3 Npl Hpl Npl many troughs abruptly terminated on up-slope end at large grabens and depressions; marked in 1 3 Npl HNade 1 Npld 1 places by dissected wrinkle ridges. Unit not recognized by Scott and Tanaka (1986). Interpreta- Depression or caldera tion: Fluvial erosion and sapping of easily eroded volcanic (possibly pyroclastic) materials or d c Hpl3 cs Dome—Interpreted as ancient volcano or older crustal materia c1 1 cs c Npl1 c2 c1 1 rock outcrops of the plateau and high-plains assemblage, which may include intermediate dis- Npld c1 c Npl c1 1 Npl Hpl 2 sected material (unit HNpld), fractured and dissected material (unit Nfd), older fractured mate- Crater rim crest cs 1 HNf 3 Ht1 c Npl1 Npld rial (unit Nf), and basement complex (unit Nb); troughs enlarged by fluvial and eolian activity 1 c 1 Nak Hpl 3 Hpl Npld and mass wasting Crater central peak Npl2 HNade c Hpl3 Hpl 3 1 cs HNpld Intermediate dissected material—Similar to younger dissected material but more well-defined Hpl3 3 cs c1 Hpl3 Crater central pit c1 5A Nah drainage systems. Unit not recognized by Scott and Tanaka (1986). Interpretation: Fluvial ero- Hpl Nfd c1 1 sion and sapping of materials, which largely include fractured and dissected material (unit ), Npl Hpl3 c1 3 2 Center of figure HNade Npl older fractured material (unit Nf), and basement complex (unit Nb), and structures along parts of ° Npld HNf 1 –45 –45 Npl HNafs ° the southern margin of the Thaumasia plateau Hpl3 Npld 1 Npld Older dissected material—Similar in occurrence and appearance to subdued cratered and cra- Npld Hpl3 c2 Hpl c1 Npl2 3 cs tered units but more highly dissected by channels and troughs; also occurs in places on ancient Hpl3 HNcht c 1 85° 80 Nak impact crater rims and near older flow and construct materials. Interpretation: Origin same as 90° ° Npl1 Hpl3 ° 75 Npld that of subdued cratered and cratered units but more eroded by fluvial and sapping processes Npld 95 ° Npl 2 c Nple Etched material—Irregular surface furrowed by sinuous, curved to flat-bottomed grooves and 1 1 Npl Npld Nah Npld 100° 70° Al troughs exhibiting irregular scarp edges. Interpretation: Material probably same as troughed c2 Hpl Hpl3 3 material but groove and trough enlargement influenced more by eolian activity and mass wast- cs 65 c Nah 105° ° 1 ing than fluvial erosion cs SCALE 1 : 4 440 910 (1 mm = 4.44091 km) AT –35° LATITUDE High-plains materials c HNafs 1 LAMBERT CONFORMAL CONIC PROJECTION Hr Younger ridged plains material—Forms smooth plains marked by long, nearly parallel, linear to ° –15° 60 c2 110 ° sinuous wrinkle ridges resembling those of lunar maria in Sinai and Coprates east provinces; –20° HNafs moderately cratered; flow margins visible in places; ridges generally trend north-northeast, are –25° –30° INTERIOR—GEOLOGICAL SURVEY, RESTON, VA—2001 tens of kilometers apart, and extend as much as 100 km; partly buries the rock surfaces and ° –50 –50 ° –35° 55 ° Prepared on behalf of the Planetary Geology and Geophysics Program, Solar System associated structures of older ridged plains material (unit HNr) in the western part of the Thau- 115 ° –40° Exploration Division, Office of Space Science, National Aeronautics and Space masia Planum province, which includes part of the ejecta blanket of impact crater centered at lat –45° Administration 21.25° S., long 73.25°, intermediate fractured material (unit HNf) in the northern part of the –50° Edited by Derrick D. Hirsch; cartography by Ralph O. Aeschliman, Jr. and Darlene A. HNt 100 0KILOMETERS 100 200 300 400 500 600 700 800 900 1000 Casebier Sinai province, and terraced material (unit ) in the northeastern part of the Thaumasia high- Manuscript approved for publication June 5, 1998 land province; gradational with the overlapping older flows of the Syria Planum Formation (unit Hsl1). Interpretation: Low-viscosity lava flows from local and regional centers, which may include the Syria Planum region; ridges mainly compressional features 65° 65° HNr Older ridged plains material—Similar to younger ridged plains material but cut by grabens and MC–1 more densely cratered; partly buries subdued cratered unit (unit Npl2), older fractured material DESCRIPTION OF MAP UNITS WESTERN VOLCANIC ASSEMBLAGE Hsu Upper member—Mottled light and dark flows form complex, interfingering, elongated tongues of the plateau and high-plains assemblage. Interpretation: Probably various materials having (unit Nf), older flow and construct material (unit Nfc), and material of degraded craters (unit c1) [Though the origin and composition of many units are obscured or controversial, interpretations are based on objective Tharsis Montes Formation—Includes lava flows of large shield volcanoes of Tharsis Montes; with distinct lobe fronts in northwest part of map region; overlaps younger flows of lower smooth surfaces at image resolution, including lava flows, and eolian, mass-wasted, and fluvial along the western margin of the Coprates province, but overlapped by younger ridged plains descriptions of morphologic characteristics visible on Viking images. Age relations are determined by stratigraphic positions members 4 and 6 (Scott and Tanaka, 1986) not present in map area member (unit Hsl2) and younger and older fractured materials (units Hf and Nf, respectively); deposits that bury most underlying rocks material (unit Hr) of Sinai province; small occurrence centered at lat 43.5° S., long 86.5°. Unit MC–2 MC–4 and crater counts (table 1). Many of the units were previously described and mapped at 1:15,000,000 scale by Scott and At5 Member 5—Forms light-colored, elongated flows with frontal lobes; overlaps member 3 (unit cut by few northwest-trending grabens of Claritas Fossae and several northeast-trending and Npl2 Subdued cratered unit—Forms highland plains characterized by subdued and partly buried older not recognized by Scott and Tanaka (1986). Interpretation: Similar to that of younger ridged MC–3 Tanaka (1986); we preserve their nomenclature and interpretations where possible] AHt3); occupies small area in northwest part of the map region. Interpretation: Lava flows of curvilinear grabens; marked in few places by chains of pit craters. Interpretation: Lava flows crater rims; cut in places by grabens; rare flow fronts; locally grades into younger (unit Hr) and plains material (unit Hr) 30° 30° CHANNEL-SYSTEM AND EOLIAN MATERIALS the region; high albedo may be produced by eolian mantle Hsl2 Younger flows of lower member—Similar to upper member but elongated tongues of flows and older (unit HNr) ridged plains materials. Interpretation: Thin layer of lava flows and fluvial and HNt Terraced material—Forms rugged, uneven plains marked by irregular scarps; also includes sub- AHt their lobe fronts are less distinct, and faulted by northwest-trending grabens of Claritas Fossae; eolian deposits that partly bury underlying rocks; colluvial materials may also be present as at dued wrinkle ridges and grabens. Partly buried by younger ridged plains material (unit Hr) and Al Linear material—Forms linear, ripplelike features in topographic low centered at lat 50.0° S., long 3 Member 3—Forms a plain of light and dark flows that overlaps member 2 (unit Ht2) and embays highland materials in the northwest part of the map region; fewer lobate fronts than the super- overlaps older flows of lower member (unit Hsl1) and younger fractured material (unit Hf). lat 42.0° S., long 55.5° gradational, in places, with older ridged plains material (unit HNr). Unit not recognized by Scott 120° 60° 66°; wavelength of ripples about 1 km. Unit originally recognized by Scott and Tanaka (1986) Interpretation: Lava flows Npl1 Cratered unit—Consists of highly cratered, rough, irregular material of moderate relief; grabens, Interpretation as unit Ae. Interpretation: Dune field posed member 5 of the Tharsis Montes Formation; cut by few northwest-trending grabens. and Tanaka (1986). : Older ridged plains material stripped and degraded by wind Hsl Older flows of lower member Interpretation Hch Channel and flood-plain material—Forms smooth channel and crater floors and outwash plain Interpretation: Lava flows of the Arsia Mons region; contrasting albedo may represent distinct 1 —Forms a relatively smooth plain unlike overlying younger flows channels, and large scarps in places. : Mixture of impact breccia, crater-rim mate- erosion and possible tectonic activity and fluvial modification (sapping) exposing older basal MC–8 MC–9 MC–10 MC–11 of lower member (unit Hsl ); flow fronts visible in places; cut by few northwest-trending gra- rials, lava flows, and sedimentary deposits, which include eolian and fluvial materials materials in places in discharge area centered at lat 39.5° S., long 104°; partly buries intermediate fractured mate- lava flow types typified by surface texture or the presence or lack of eolian mantles 2 bens of Claritas Fossae; overlaps younger fractured material (unit Hf) and younger ridged plains Nplh HNu Undivided material rial (unit HNf); abruptly terminated on upslope end near graben. Interpretation: Channel mate- Ht2 Member 2—Forms a relatively smooth plain of flows having broad, subdued, lobate fronts; fewer Hilly unit—Forms mesas, knobs, and broad areas that rise above surrounding materials; marked —Forms rugged walls interrupted by spurs and gullies of fronts than the overlying member 3 of the Tharsis Montes Formation; cut in few places by material (unit Hr) and embays highland materials along part of northern margin of Thaumasia in few places by large ridges and scarps as at lat 28.0° S., long 110.5°. Embayed and (or) partly and large depressions along northeast edge of map region. Interpretation: Basement, most of 180° rial deposited by discharge of ground water via graben 135° 90° 45° 0° highland province. Interpretation: Lava flows subdued by eolian deposition and erosion buried by material of several younger units of the plateau and high-plains assemblage. Interpre- plateau sequence, intermediate fractured material, and ridged plains materials exposed by fault- 0° 0° HNcht Chaotic material—Forms irregular patches of closely spaced knobs of similar heights; occurs northeast-trending grabens; overlaps member 1 (unit Ht1) and intermediate fractured material near highly faulted and dissected areas and within impact crater. Unit not recognized by Scott (unit HNf) and embays highland materials along part of the western margin of the Thaumasia Flow and construct materials tation: Impact breccia, volcanic materials, and possibly older crustal materials; high elevation ing and erosion including slumping, mass-wasting, and sapping highland province. Interpretation: Lava flows of the Arsia Mons region Younger flow and construct material—Forms mountains of high relief in the southwest part of caused by tectonic uplift and impact-basin formation during period of heavy bombardment and Tanaka (1986). Interpretation: Erosional remnants formed by disruption of terrain by HNfc CIRCUM-ARGYRE MATERIALS Ht Member 1—Forms a relatively smooth to hummocky plain in southwest part of the map region the Thaumasia highlands province; radial channels and dissecting grabens common, central MC–16 MC–17 MC–18 MC–19 ground-water release and tectonic activity or by mass wasting 1 Fractured materials—The origin and rock type of these units are only inferred because fractures that is cut by northeast-trending grabens; flow fronts rare; partly buries intermediate fractured depressions less common; lobate fronts in places; flat-floored troughs and lobate scarps may be and grabens have obscured original surface characteristics in most instances. Interpretation: [Consists of units in northwest part of ] VALLES MARINERIS INTERIOR DEPOSITS material (unit HNf) and in places, wrinkle ridges of an older, underlying surface. Interpretation: present on or near some of the mountain flanks as at lat 40.5° S., long 101.0° similar to those of The units consist of impact breccia, crater-rim materials, lava flows, and sedimentary deposits, HNafs Smooth floor unit—Forms areas of smooth, relatively featureless plains in valleys that trend 120° 60° Avfs Smooth floor material—Occurs along canyon floors as smooth to undulatory materials of low Lava flows of the Arsia Mons region Apollinaris and Hadriaca Paterae. Unit not recognized by Scott and Tanaka (1986). Interpreta- which include eolian and fluvial materials. Faults caused by crustal extension and warping downslope toward basin floor of Argyre Planitia. Embays and partly buries basin-rim unit of relief. Interpretation: Primarily eolian and colluvial deposits Syria Planum Formation—Includes lava flows that originated from northern Syria Planum and tion: Volcanoes and lava flows and (or) eroded high-standing outcrops of plateau material in Hf Younger fractured material—Forms relatively smooth surfaces in northwest part of the map Argyre (unit Nah). Unit not recognized by Scott and Tanaka (1986). Interpretation: Probably places –30° –30° Avfr Rough floor material—Forms rough surface of canyon floor centered at lat 16.0° S., long 57.3°. regions (north of the northwest part of the map region). Lower member of region; moderately cut by northwest-trending grabens. Embays older fractured material (unit sedimentary deposits of eolian, mass-wasted, fluvial, and possibly glacial origin in structurally MC–25 Interpretation: Mixture of landslides and debris flows from canyon walls and eolian deposits Scott and Tanaka (1986) divided into younger and older flows Nfc Older flow and construct material—Forms conical mountains in parts of the Thaumasia high- Nf), basement complex (unit Nb), and older flow and construct material (unit Nfc) but partly controlled valleys primarily formed by the Argyre impact event lands that partly resemble younger flow and construct material (unit HNfc), but larger relief and HNade MC–24 MC–26 buried by lava flows of the Syria Planum Formation Dissected and etched unit—Moderately cratered plateau surface marked by large valley forms, more highly cratered; may be embayed by Noachian and (or) Hesperian materials. Unit not rec- HNf Intermediate fractured material—Forms relatively smooth surfaces of moderate relief with irregular depressions, drainage basins comprising valley networks, and highly subdued ridges ognized by Scott and Tanaka (1986). Interpretation: Ancient volcanoes and (or) eroded high- fractures and grabens; moderately cratered. Overlies other highly deformed terrain materials but of all shapes and sizes. Surface also furrowed in places by sinuous, intersecting, curved to flat- standing outcrops of plateau material in places is embayed and partly covered by older flows of lower member of Syria Planum Formation bottomed grooves, producing an etched or sculptured surface. Unit not recognized by Scott and (unit Hsl1), younger ridged plains material (unit Hr), members 3, 2, and 1 of Tharsis Montes Tanaka (1986). Interpretation: Cratered unit, which may locally include ejecta materials related MC–30 PLATEAU AND HIGH-PLAINS ASSEMBLAGE Formation (units AHt , Ht , and Ht , respectively), and smooth unit of plateau sequence (unit to the Argyre impact, partly mantled by eolian, alluvial, and colluvial deposits that have been Any use of trade, product, or firm names in this publication is for –65° –65° GEOLOGIC MAP OF THE THAUMASIA REGION, MARS 3 2 1 [Forms ancient highland terrain and local tracts of younger deposits] Hpl descriptive purposes only and does not imply endorsement by the 3). Unit not recognized by Scott and Tanaka (1986) modified by eolian, mass-wasting, sapping, fluvial, and (or) possibly glacial resurfacing U.S. Government. Plateau sequence Nfd Fractured and dissected material—Similar to older fractured material but dissected by small Nak Knobby unit—Forms irregular clusters of abundant small, knoblike hills that in part resemble QUADRANGLE LOCATION By For sale by U.S. Geological Survey, Information Services, Box 25286, Hpl Smooth unit—Occurs mainly in southern half of map region as large areas of flat, relatively fea- valleys, valley networks, and troughs; marked in places by triangular-shaped scarps, tilted beds, chaotic material. Unit not recognized by Scott and Tanaka (1986). Interpretation: Knobby Federal Center, Denver, CO 80225, 1–800–ASK–USGS Photomosaic location is shown in the western hemisphere of 3 Mars. An outline of 1:5,000,000-scale quadrangles is James M. Dohm, Kenneth L. Tanaka, and Trent M. Hare tureless plains; in places forms smooth to moderately rough floors of some impact craters, cut and ridges along parts of southern margin of the Thaumasia plateau. Unit not recognized by material formed by eolian, fluvial, and possibly glacial erosion of basin-rim unit (unit Nah) or provided for reference. 2001 by grabens, and marked by subdued wrinkle ridges; embays rock outcrops of several older units Scott and Tanaka (1986). Interpretation: Origin same as that of older fractured material but cratered unit (unit Npl1) or by tectonic activity related to impact-basin formation Printed on recycled paper